An epoxy resin is the resin which has more than two epoxy groups (—CH(O)CH2) in the molecule. An epoxy resin affords a cured resin excellent in dielectric ability, mechanical strength, dimensional stability, and chemical resistance when it is cured by combining a suitable curing agent. An epoxy resin therefore has variety of applications such as a paint for metal, an anticorrosion material, an adhesive, a structural material reinforced by glass fibers, and the like.
J. Polymer Sci. Part A-1, 4, 751 (1966), Iwakura et al, describes an oxazolidone ring-containing epoxy resin. The oxazolidone ring-containing epoxy resin is that obtained by allowing a blocked diisocyanate compound which is obtained by reaction of diisocyanate and monoalcohol, to react with a diepoxy compound. J. Appl. Polymer Sci., 9, 1984 (1966), Sander et al, for example describes an oxazolidone ring-containing epoxy resin which is obtained by allowing a diisocyanate compound to directly react with a diepoxy compound.
The epoxy resins may be employed as a binder resin for an aqueous coating composition. In this instance, an ionic grouup is introduced in the epoxy resins to provide hydrophilic epoxy resins. Japanese Patent Laid Open Publication No. 306327/1993 describes the method of that a terminal epoxy group of the oxazolidone ring-containing epoxy resin prepared by the above described means, is ring-opened with an active hydrogen compound having an ionic group to prepare an oxazolidone ring-containing aqueous resin having an ionic group such as an amino group, and a carboxyl group therein. This publication also describes an aqueous coating composition which comprises such an oxazolidone ring-containing epoxy resin.
Corrosion resistance, impact resistance, cohesiveness, excellent appearance, and the like are generally required for a resin for use in a coated film. An oxazolidone ring-containing epoxy resin is excellent in heat resistance, and corrosion resistance, and therefore affords a coated film excellent in heat resistance, and corrosion resistance. However, the conventional oxazolidone ring-containing epoxy resin is poor in flexibility. Therefore, impact resistance of a coated film becomes poor when the oxazolidone ring-containing epoxy resin is used as a resin for a coated film.